1. Field of the Invention
The present invention relates to a position detecting method and a position detecting device and, in particular, to a position detecting method and a position detecting device according to which, in an exposure device for manufacturing semiconductor devices, relative positioning (i.e., alignment) is effected between a first object, e.g., one consisting of a minute electronic circuit pattern, such as an IC, LSI or VLSI formed on a reticle or a mask surface, and a second object, e.g., one consisting of a wafer.
2. Description of the Related Art
As integrated circuits increase in density, a projection exposure device for manufacturing semiconductor devices is required to be capable of performing projection exposure of a circuit pattern onto a reticle surface with higher resolution. To improve the projection resolution of the exposure device, the wavelength of the exposure light is fixed and the NA (numeral aperture) of the projection optical system is increased, or the wavelength of the exposure light is shortened. For example, the wavelength is changed from that of the g-line to that of the i-line or from the wavelength of the i-line to that of an excimer laser.
Further, as the circuit pattern becomes more minute, there is a demand for more accurate alignment of the circuit pattern formed on the reticle and the pattern on the wafer. The alignment between the reticle and the wafer is effected either by using exposure light, to which the resist applied to the wafer surface is exposed, or by using non-exposure light, to which the resist is not exposed. An example of non-exposure light is light having a wavelength of 633 nm, which is the oscillation wavelength of a HeNe laser. Nowadays, the method using non-exposure light is mostly adopted due to the fact that it is advantageously not liable to be influenced by the semiconductor process.
The present applicant has proposed alignment devices using non-exposure light in Japanese Patent Laid-Open Nos. 63-32303, 2-130908, etc., which have been realized as products with recognized advantages. The method is called the TTL-off-axis system, in which the pattern on the wafer is observed with non-exposure light through the projection optical system for transfer-projecting the pattern of the reticle onto the wafer. During observation, the chromatic aberration generated by the projection optical system at the wavelength of non-exposure light is corrected by an alignment optical system. In another system, which is called the non-TTL-off-axis system, the wafer is observed for alignment with a completely independent optical system (off-axis microscope) without involving the projection optical system at all.
As is the case with the above applications, most of the alignment systems currently in use adopt a so-called image processing method, in which an image of a position detecting mark (alignment mark) on the wafer is formed on an image pickup device such as a CCD camera, and an electrical signal obtained from the image pickup device is processed to thereby detect the position of the wafer.
However, when the above-described position detecting method is applied to an X-ray exposure device using a proximity gap, it is difficult to simultaneously detect the optical image of the position detecting mark on the mask and the optical image of the position detecting mark on the wafer due to the presence of a gap between the mask and the wafer.
It is accordingly an object of the present invention to provide a position detecting device which is capable of detecting the relative positions of two objects spaced apart from each other in the optical-axis direction of the detection optical system, as in the proximity method, with high accuracy by the image processing method, and a semiconductor device manufacturing method using this device.
In view of the foregoing, in one aspect, the present invention relates to a position detecting device for detecting relative positions of first and second objects each equipped with a position detecting mark, the device comprising a reference member equipped with separate alignment marks corresponding to the position detecting marks of the first and second objects, respectively; and an image pickup system for simultaneously taking images of the position detecting marks of the first and second objects and the alignment marks corresponding thereto.
In another aspect, the present invention relates to a position detecting device for detecting a positional relationship between first and second objects arranged opposite to each other by using a first position detecting mark arranged on the first object and a second position detecting mark arranged on the second object, the position detecting device comprising a first illumination system for illuminating the first position detecting mark and the second position detecting mark, a reference member having alignment reference marks corresponding to the first and second position detecting marks, a second illumination system for illuminating the alignment reference marks, and an image taking system for taking optical images of the first and second position detecting marks and optical images of the alignment reference marks, wherein a positional relationship between the optical image of the first position detecting mark and the optical images of the alignment reference marks of the reference member is detected by using the image taking system, and wherein a positional relationship between the optical image of the second position detecting mark and the optical images of the alignment reference marks is detected by using the image taking system, whereby the detection of the relative positions of the first and second objects is executed.
In yet another aspect, the present invention relates to a method for detecting relative positions of first and second objects each equipped with a position detecting mark, the method comprising the steps of preparing separate reference alignment marks on a predetermined member, the alignment marks respectively corresponding to the position detecting marks of the first and second objects, and simultaneously taking images of the position detecting marks of the first and second objects and the alignment marks to obtain information on the relative positions of the first and second objects.
In yet a further aspect, the present invention relates to a position detecting method for detecting a positional relationship between first and second objects arranged opposite to each other by using a first position detecting mark arranged on the first object and a second position detecting mark arranged on the second object, the method comprising the steps of providing alignment reference marks on a predetermined reference member, the alignment reference marks respectively corresponding to the first and second position detecting marks, and taking optical images of the first and second position detecting marks and the alignment reference marks, wherein a positional relationship between the optical image of the first position detecting mark and the optical images of the alignment reference marks is detected by the image taking, and wherein a positional relationship between the optical image of the second position detecting mark and the optical images of the alignment reference marks is detected by the image taking, whereby the detection of the relative positions of the first and second objects is executed.
In still another aspect, the present invention relates to an exposure device for transferring a pattern of a first object through exposure onto a second object after performing alignment of the first and second objects, which objects are arranged opposite to each other, by detecting a positional relationship between the first and second objects by using a first position detecting mark arranged on the first object and a second position detecting mark arranged on the second object, the exposure device comprising a first illumination system for illuminating the first position detecting mark and the second position detecting mark, a reference member having alignment reference marks respectively corresponding to the first and second position detecting marks, a second illumination system for illuminating the alignment reference marks, and an image taking system for taking optical images of the first and second position detecting marks and optical images of the alignment reference marks, wherein a positional relationship between the optical image of the first position detecting mark and the optical images of the alignment reference marks is detected by using the image taking system, and wherein a positional relationship between the optical image of the second position detecting mark and the optical images of the alignment reference marks is detected by using the image taking system, whereby the detection of the relative positions of the first and second objects is executed.
In yet a still further aspect, the present invention relates to a device manufacturing method comprising (a) a position detecting process for detecting the positional relationship between first and second objects arranged opposite to each other by using a first position detecting mark arranged on the first object and a second position detecting mark arranged on the second object, the position detecting process comprising the steps of (1) providing alignment reference marks on a predetermined reference member, the alignment reference marks respectively corresponding to the first and second position detecting marks, and (2) taking optical images of the first and second position detecting marks and optical images of the alignment reference marks, wherein a positional relationship between the optical image of the first position detecting mark and the optical images of the alignment reference marks is detected the image taking, and wherein a positional relationship between the optical image of the second position detecting mark and the optical images of the alignment reference marks is detected by the image taking, whereby the detection of the relative positions of the first and second objects is executed, and (b) an exposure process for transferring the pattern of the first object through exposure onto the second object after alignment of the first object with the second object whose relative positions have been detected by the position detecting process, a device being formed by using the pattern exposed and transferred by the exposure process.
In another aspect, the present invention relates to a device for detecting alignment, in an optical axis direction, of a mask having a mask alignment mark and a wafer having a wafer alignment mark, the mask and the wafer being arranged along the optical axis spaced apart from and facing one another, the device comprising a plate separate from the mask and a wafer reference mark, an optical system for illuminating the mask alignment mark of the mask and the wafer alignment mark of the wafer with a first light source and for illuminating the mask reference mark of the plate and the wafer reference mark of the plate with a second light source separate from the first light source, and for forming images of the mask alignment mark and the mask reference mark on a first image pickup device and for forming images of the wafer alignment mark and the wafer reference mark on a second image pickup device separate from the first image pickup device, and a detector for detecting a first positional deviation between the mask alignment mark and the mask reference mark on the basis of a signal from the first image pickup device corresponding to the images thereof, for detecting a second positional deviation between the wafer alignment mark and the wafer reference mark on the basis of a signal from the second image pickup device corresponding to the images thereof, and for detecting a positional deviation in the optical axis direction between the mask and the wafer in accordance with the first and second positional deviations.
In still another aspect, the present invention relates to a position detecting apparatus for detecting relative positions of a mask equipped with mask position detecting mark and a wafer equipped with a wafer position detecting mark, the apparatus comprising means for illuminating the mask position detecting mark and the wafer position detecting mark to form images thereof on separate first and second image pickup devices, respectively, a plate having first and second alignment marks separated by a predetermined distance, means for illuminating the first and second alignment marks to form images thereof on the first and second image pickup devices, respectively, and means for determining a first positional deviation between the images of the mask position detecting mark and the first alignment mark in accordance with a signal from the first image pickup device, for determining a second positional deviation between the images of the wafer position detecting mark and the second alignment mark in accordance with a signal from the second image pickup device, and for determining a positional deviation of the mask and the wafer in accordance with the first and the second positional deviations and the predetermined distance between the first and second alignment marks.
These and other aspects, objects, advantages, and features of the present invention will become apparent from the following detailed description of preferred embodiments thereof taken in connection with the accompanying drawings.